Impacts of Ultraviolet Radiation on Aquatic Ecosystems: Greenhouse Gas Emissions and Implications for Hydroelectric Reservoirs

Abstract

Ultraviolet radiation (UV) affects carbon dynamics in aquatic ecosystems. Photooxidation of dissolved organic matter (DOM) can produce greenhouse gases (GHG) and the effects of UV on primary and secondary production can influence the flux of carbon (C) between aquatic ecosystems and the atmosphere. Products of photooxidation include: DOM of lower molecular weight, carbon dioxide (CO₂) and carbon monoxide (CO). Lower molecular weight DOM can be more easily utilized by microorganisms. Secondary microbial production and the production of CO₂ from aerobic respiration are, therefore, favored. However, the harmful effects UV have on phytoplankton diminish the rate of CO₂ fixation. The fluxes of CO₂ in reservoirs are influenced in the same manner as natural lakes since reservoirs older than 10 years are comparable to lakes. The largest distinction to be made between reservoirs and lakes is their surficial aerial coverage, which is generally much larger for reservoirs. This factor may help explain the differences observed in carbon fluxes from natural lakes and reservoirs. Following the literature review, a first gross estimate was made of the importance of the production of GHGs resulting from photooxidation relative to other processes. The results show that when making a calculation of the balance of net CO₂ emissions from aquatic ecosystems and hydroelectric reservoirs, photooxidation needs to be taken into consideration as it can account for between 6 and 28% of total emissions.